The present invention relates generally to the field of packaging bags, and more particularly, to a new and improved method of manufacturing packaging bags.
Numerous packaging bags and numerous systems for manufacturing them have already been proposed.
For bags of small thickness, i.e. that are generally flat in the filled state, known means generally give satisfaction. Under such circumstances, the bags are generally formed using two plane sheets that are bonded together along three sides and that are provided with closure means, e.g. complementary male/female strips, at the mouth of a bag.
In contrast, until now, making bags that are intended to receive contents that are thick, has turned out not to be entirely satisfactory, even though a large amount of research has been performed in this very specific field.
In particular, such bags often require lateral bellows which are difficult to make.
Accompanying FIG. 1 shows, diagrammatically, a known technique for making bags with lateral bellows by inserting pre-formed bellows 10 between two sheets 12 and 14 that constitute two main faces of the bags, with the bellows being inserted at 90xc2x0 to the travel direction S of said sheets. Said sheets 12 and 14 are provided with longitudinal male/female closure strips 13 and 15. The bellows 10 are preferably of varying width, increasing away from the closure strips 13 and 15 so as to enable the bags to be inflated. That known technique does indeed make it possible to make packaging bags having lateral bellows. Nevertheless, it turns out to be quite complex. In particular, the need to insert the bellows 10 at 90xc2x0 to the travel direction of the sheets 12 and 14 does not enable high manufacturing throughputs to be obtained, and requires insertion of the bellows 10 to be adequately synchronized with the travel of the sheets 12 and 14.
Document FR-A-2 686 063 describes another technique of manufacturing packaging bags with bellows that consist in preforming a bag with lateral bellows, in splitting the bag over a portion of its length along fold lines external to the bellows, in folding the flaps defined in this way back over the outside of the bag, in placing the closure strips on said flaps, in reforming the bag, and in bonding the closure strips to said flaps that have been put into place. Unfortunately, because of its complexity, that technique does not give full satisfaction.
The Applicant has also described various alternative solutions for manufacturing packaging bags with lateral bellows in French patent application No. 96 02389 filed on Feb. 27, 1996.
The present invention seeks to improve upon the known means for manufacturing packaging bags having lateral bellows.
The aforenoted object is achieved in the context of the present invention by a method of manufacturing packaging bags characterized by the fact that it comprises the steps of:
forming respective cutouts in each of the two lateral, bellows-forming zones of a packaging bag sheet so that the bag has only two thicknesses superposed at the mouth of said bellows, at least over a portion of its width; and
heat-sealing the adjacent edges of the sheet to the peripheries of the cutouts to close the bag.
The present invention also provides apparatus for implementing the method, and bags obtained thereby.